Vehicle designers are continually seeking techniques for increasing the efficiency of vehicle operation. Some improvements have been made to use less energy during vehicle operation, while other improvements seek to recover energy expended or lost during vehicle operation. For example, approximately sixty-eight percent of the energy provided from vehicle fuel is lost through inefficiencies of an internal combustion engine, some of which are in the exhaust system, with that loss being in the form of heat. Since energy loss is undesirable, it would be advantageous to recover some of the heat energy that conventionally is wasted during vehicle operation.
A Stirling engine operates via a temperature difference between a hot side and cool side of the engine. FIGS. 1-4 are partial cut-away views that illustrate the basic operation of a conventional Stirling engine. Referring to FIG. 1, the Stirling engine 10 is shown in the contraction phase. A cylinder 12 is positioned having a heat source 14 on one end of the cylinder 12 and a cooling source 16 on an opposite end. A piston 18 is made to move within the cylinder 12 due to the heating and cooling of gases 24 within the cylinder 12. A displacer 22 assists in moving the gases 24 between the heat source 14 (the hot side of the Stirling engine 10) and the cooling source 16 (the cool side of the Stirling engine 10). The piston 18 is coupled to a flywheel (not shown) via a shaft 20 allowing the Stirling engine 10 to produce work via the oscillation of the piston 18 within the cylinder as is commonly known. One form of work for a Stirling engine is to convert the mechanical movement of the piston 18 into electrical energy by driving a generator from the Stirling engine 10.
In the contraction phase, the gases 24 have collected near the cooling source 16 and are contracting due to the extraction of heat from the gases. The cooling source 16 may be a heat sink (e.g., cooling fins) or an active cooling source such as a cooling fluid pumped around the cool end of the Stirling engine 10. The contracting gases 24 draw the piston 18 into the cylinder 12 as indicted by the arrow 26.
Referring now to FIG. 2, the transfer stage of the Stirling engine 10 is illustrated. In the transfer stage, the displacer 22 moves toward the cool side of the Stirling engine 10 (as indicated by the arrow 28), which drives the gases 24 toward the hot side of the Stirling engine. This positions the gases 24 over the heat source 14 so that they can be heated in the expansion phase, which is illustrated in FIG. 3.
As illustrated in FIG. 3, the gases 24 expand upon being heated by the heat source 14. The heat source 14 can be any heat source, including but not limited to, a fuel burner or the exhaust gases of a fuel burning engine such as an internal combustion engine. The expanding gases 24 drive the piston 18 outward as indicated by the arrow 30.
Referring now to FIG. 4, the final stage of operation for a Stirling engine is to again transfer the gases 24. In this transfer stage, the displacer 22 is moved (as indicated by the arrow 32) into the cylinder 12 via the flywheel (not shown), which forces the gases 24 toward the cool side of the Stirling engine 10 so that the cycle may repeat beginning again as described in connection with FIG. 1.
Thus, a Stirling engine could be utilized to recover some of the otherwise wasted heat energy in the exhaust system of contemporary motor vehicles. However, contemporary vehicles are subject to emission control standards that must be maintained during the operation of the vehicle. Some emission control systems must achieve a certain operational temperature to be fully effective, and this operational temperature is commonly achieved by being heated by the exhaust gases. Therefore, a Stirling engine could recover so much heat energy from the exhaust gases that the emission control system does not achieve the intended operational temperature to be effective at maintaining emission control standards during vehicle operation.
Accordingly, it would be desirable to provide a system and method for incorporating a Stirling engine into a vehicle for electrical power generation, while maintaining vehicle emissions requirements. Additionally, other desirable features and characteristics of the present disclosure will become apparent from the subsequent description taken in conjunction with the accompanying drawings and the foregoing technical field and background.